Polishing pad of a polyurethane of propane diol

ABSTRACT

This invention is directed to a polishing pad for chemical mechanical polishing of substrates, for example, the surface of electrical devices such as semiconductors or other substrates; wherein the pad comprises a polyurethane that is the reaction product of an organic polyisocyanate and 1,3 propane diol; preferably, the pad has a porous structure and more preferably has a microporous structure.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of provisional application 60/206,244 filed May 23, 2000.

FIELD OF THE INVENTION

[0002] This invention relates to a polishing pad for polishing and planarizing the surface of electrical devices such as semiconductor devices, integrated circuit wafers and other surfaces such as high-purity quartz substrates and silicon wafers.

DESCRIPTION OF RELATED ART

[0003] Peters U.S. Pat. No. 3,180,853 issued Apr. 27, 1965 discloses elastomeric chain extended urethanes polymers useful for forming porous and non porous shaped structures. Hollowell U.S. Pat. No. 3,067,482 issued Dec. 11, 1962 discloses non-woven sheet materials impregnated with a polymeric material. Yuan U.S. Pat. No. 3,190,766 issued Jun. 22, 1965 and Holden U.S. Pat. No. 3,208,875 issued Sep. 28,1965 discloses forming a microporous sheet material of a nonwoven substrate coated with a microporous polymeric layer. Hulslander et al U.S. Pat. No. 3,284,274 issued Nov. 8, 1966 discloses a sheet material of a non-woven substrate coated with a microporous layer having a vertical elongated pore structure. This material was used as a polishing pad for polishing electrical devices such as semiconductor devices.

[0004] Polishing pads for polishing and planarizing surfaces of electrical devices such as semiconductor devices and the like are disclosed in the following patents: Hoffstein et al U.S. Pat. No. 4,841,680 issued Jun. 27, 1989; Budinger et al U.S. Pat. No. 4,927,432 issued May 22, 1990; Hyde et al U.S. Pat. No. 5,257,478 issued Nov. 2, 1993; Cook et al U.S. Pat. No. 5,489,233 issued Feb. 6, 1996; Reinhardt et al U.S. Pat. No. 5,578,362 issued Nov. 26, 1996; Roberts U.S. Pat. No. 5,605,760 issued Feb. 25, 1997; Budinger et al U.S. Pat. No. 5,900,164 issued May 4, 1999; Cook et al U.S. Pat. No. 6,017,265 issued Jan. 25, 2000; Roberts et al U.S. Pat. No. 6,019,666 issued Feb. 1, 2000; Roberts et al U.S. Pat. No. 6,022,268 issued Feb. 8, 2000; Cook et al U.S. Pat. No. 6,022,264 issued Feb. 8, 2000; Cook et al U.S. Pat. No. 6,030,899 issued Feb. 29, 2000; and Cook et al U.S. Pat. No. 6,036,579 issued Mar. 14, 2000.

[0005] While these polishing pads are acceptable for many applications, it would be desirable to form a polishing pad having improved stretch recovery, a softer texture, improved abrasion resistance and an improved removal rate. It would also be desirable to form a pad that can be printed, that has improved resiliency which is expected to improve pad life, that has higher wet strength when used with aqueous slurries and that has improved toughness in comparison to polishing pads made with conventional glycol or diol components.

SUMMARY OF THE INVENTION

[0006] This invention is directed to a polishing pad for chemical mechanical polishing of substrates and in particular to polishing and planarizing the surface of electrical devices; wherein the pad comprises a polyurethane that is the reaction product of an organic polyisocyanate and 1,3 propane diol. The polyurethane can be chain extended with a dihydroxy organic compound, a diamine or an amine/hydroxy terminated organic compound. Preferably, the polishing pad has a porous structure and more preferably has a microporous structure.

DETAILED DESCRIPTION

[0007] The polishing pad of this invention is useful for polishing and planarizing the surface of a wide variety of electrical devices such as semiconductor devices, silicon wafers used in semiconductors, glass or quartz used in the formation of photo masks used to make semiconductors and the like. The polishing pad has the following advantages: improved stretch recovery, a softer texture, improved abrasion resistance, an improved removal rate of material, improved resiliency which is expected to improve pad life, higher wet strength when used with aqueous slurries, improved toughness in comparison to polishing pads made with conventional glycol or diol components. Also, the pad can be printed which allows for the incorporation of additional features on the pad surface.

[0008] The polyurethane used to form the pad is the reaction product of an organic diisocyanate and 1,3 propane diol. A chain extended polyurethane can be used wherein an isocyanate prepolymer is first formed by reacting an excess of diisocyanate with the diol and then the prepolymer is chain extended. Generally, to form the prepolymer, 2 moles of diisocyanate are used to one mole of 1,3 propane diol.

[0009] Typical compounds used to chain extend the prepolymer are organic dihydroxy compounds, diamines or a hydroxy/amine terminated compound. 1, 3 propane diol also can be used as a chain extender. Optionally, an isocyanate terminated prepolymer can be formed by using a polyol other than 1,3 propane diol and then the prepolymer is chain extended with 1,3 propane diol.

[0010] Typical organic diisocyanates that can be used are aliphatic, aromatic and cycloaliphatic diisocyanates. Typically useful diisocyanates are as follows: tolylene 2,4 diisocyanate, tolylene 2,6 diisocyanate, m-phenylene diisocyanate, biphenylene 4,4' diisocyanate, methylene bis (4 phenyl isocyanate), 4 chloro-1,3-phenylene diisocyanate, naphthalene-1,5-diisocyanate, tetramethylene-1,4-diisocyanate, hexamethylene-1,6-diisocyanate, decamethylene-1,10-diisocyanate, cyclohexylene-1,4-diisocyanate, methylene bis (4 cyclohexyl isocyanate), and tetrahydronaphthalene diisocyanate.

[0011] Typically useful chain extenders are as follows: polyalkyleneether glycols having a weight average molecular weight of about 300-5000 such as polyethyleether glycol, polypropyleneether glycol, polytetramethyleneether glycol, polyhexamethyleneether glycol, polyoctamethyleneether glycol, polynonamethyleneether glycol, polydecamethyleneether glycol, polydodecamethyleneether glycol and any mixtures of these glycols.

[0012] Hydroxyl terminated polyesters also can be used as chain extenders instead of or in conjunction with the aforementioned polyalkyleneether glycols and are formed by reacting acids, esters or acid halides with glycols. Suitable glycols that can be used are polyalkylene glycols such as methylene, ethylene, propylene, tetramethylene, decamethylene glycols, substituted polymethylene glycols such as 2,2-dimethyl-1,3-propanediol, cyclic glycols such as cyclohexanediol, and aromatic glycols such as xylylene glycol. These glycols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or lower alkyl ester or ester forming derivatives to produce relatively low molecular weight polymers like those indicated above for the polyalkyleneether glycols. Acids for preparing such polyesters are for example, succinic, adipic, suberic, sebacic, terephthalic and hexahydroterephthalic acids and the alky and halogen substituted derivatives of these acids.

[0013] Amine terminated compounds also can be used as chain extenders. One useful chain extender of this type has the formula

[0014] where R¹, R² and R³ are each a saturated aliphatic group containing 1-4 carbon atoms (i.e. methyl, ethyl, propyl or butyl group). Preferably, R³ is methyl and R¹ and R² are propyl, with the preferred compound being N-methyl-amino-bis-propyl amine. Other chain extenders that can be used are hydrazine, mono-substituted hydrazines, dimethyl-pirperazine, 4-methyl-m-phenylene-diamine, m-phenylene-diamine, 4,4' diamino-diphenyl-methane, 1,4-diaminopiperazine, ethylene diamine and any mixtures of the above compounds.

[0015] Chain extenders are used to increase and regulate the molecular weight of the polyurethane used to form the polishing pad of this invention. Typical chain extension reactions when using diamines are carried out at ambient temperatures taking care to control the temperature by the rate of addition of the diamine or by cooling since the reaction is exothermic. If glycols or diols are used as chain extenders, the reaction temperature is held at about 60-80 C. Chain terminators can be used such as monoamines or mono-alcohols to terminate the chain extension reaction and thereby control the molecular weight of the polyurethane.

[0016] Typical methods for making microporous sheet materials with the aforementioned polyurethanes that are useful as polishing pads are shown in Holden U.S. Pat. No. 3,208,875 and Hulslander et al U.S. Pat. No. 3,284,274. These polyurethanes can be formed into polishing pads containing microelements as shown in Reinhardt et al U.S. Pat. No. 5,578,362 and Budinger U.S. Pat. No. 5,900,164 and into polishing pads have a three dimensional surface texture as shown in Cook et al U.S. Pat. No. 6,022,264.

EXAMPLE

[0017] A chain extended polyurethane can be prepared as follows:

[0018] Polybutylene adipate and 1,3 propane diol (in a 1:1 molar ratio) were dissolved in DMF (dimethyl formamide having a low moisture content). MDI [methylene bis (4 phenyl isocyanate)] was added in equal molar amounts to the above solution. About 80% by weight of the MDI was added with constant stirring while controlling the temperature of the exothermic reaction. The remainder of the MDI was added with stirring to form a polyurethane solution having a solids content of about 25% by weight.

[0019] A needled web of polyethylene terephthalate fibers was impregnated with the above prepared polyurethane solution and then passed into a water/DMF bath to coagulate the polymer. The resulting porous substrate was dried and buffed to a thickness of about 50 mils. Polishing pads were then cut from the resulting porous substrate and mounted on a conventional polishing machine and used to polish silicon wafers and conventional semiconductors. The polishing results were excellent. Planarization was good, scratches and imperfections were at a minimum and the surface had excellent smoothness. 

What is claimed is:
 1. A polishing pad for chemical mechanical polishing substrates; wherein the pad comprises a polyurethane comprising the reaction product of an organic polyisocyanate and 1,3 propane diol.
 2. The polishing pad of claim 1 wherein the polyurethane has a porous structure.
 3. The polishing pad of claim 2 wherein the polyurethane has a microporous structure.
 4. The polishing pad of claim 1 in which the polyurethane consists essentially of the reaction product of an aromatic diisocyanate and 1,3 propane diol.
 5. The polishing pad of claim 2 in which the polyurethane consists essentially of an isocyanate terminated polyurethane prepolymer of an organic diisocyanate and a diol and chain extended with 1,3 propane diol.
 6. The polishing pad of claim 5 in which the isocyanate terminated prepolymer consists of the reaction product of an aromatic diisocyanate and 1,3 propane diol.
 7. The polishing pad of claim 2 in which the polyurethane consists essentially of an isocyanate terminated prepolymer of an aromatic diisocyanate and 1,3 propane diol that is chain extended with a compound selected from the group of dihydroxy terminated organic compound, a diamine and a hydroxy/amine terminated organic compound.
 8. The polishing pad of claim 2 in which the polyurethane consist essentially of the reaction product of methylene bis (4 phenyl isocyanate) and a mixture of 1,3 propane diol and polybutylene adipate.
 9. The polishing pad of claim 2 for polishing and planarizing the surface of electrical devices in which the polyurethane consists of the reaction product of an aromatic diisocyanate, 1,3 propane diol chain extended with a diamine.
 10. The polishing pad of claim 2 for polishing and planarizing the surface of electrical devices in which the polyurethane consists of the reaction product of an aromatic diisocyanate, 1,3 propane diol and an ester and is chain extended with a diamine.
 11. A process for chemical mechanical polishing of substrates which comprises contacting the substrate with a polishing pad and having a polishing slurry at the interface of the substrate and the polishing pad; wherein the pad is formed from a polyurethane comprising the reaction product of an organic polyisocyanate and 1,3 propane diol. 